In the art of respiratory masks it is well known to provide masks of various sorts as part of a gaseous medium delivery system for delivering a respiratory gas to the airway of a user. Such masks commonly have included a mask shell member which confronts and encloses a portion of the user's face, and a perimeter seal which engages the user's face to seal the interface between the user's face and the mask shell. The seal is particularly important for those uses in which the mask serves to deliver a gaseous medium at elevated pressure to the user. Typically, at any given time the gas pressure is intended to be at a specified magnitude. Management of the gas pressure magnitude would be seriously complicated by improper sealing and resulting uncontrolled leakage from the mask.
The technology is replete with examples of such masks, including U.S. Pat. Nos. and publications 3,680,555, 3,545,436, H397, 4,989,596, 4,440,163, 4,971,051, 2,671,445, 4,905,683, 4,739,755, 4,296,746, and 3,330,273. Each of the cited documents discloses a mask structure for the delivery of a gaseous medium to a user, or a seal structure for such a mask. In particular, some of the cited art discloses generally inturned seal elements extending about the perimeter of a mask shell.
Respiratory masks often are utilized on a relatively long term continuous basis so that user comfort and tolerance become crucial considerations in the mask design. To maximize user comfort and tolerance, the mask must be of minimal weight. It also needs to be well ventilated to carry moisture away from the facial area of the user. In addition, the shape, form and material of the mask (i.e. whether opaque versus transparent) can significantly influence the likelihood of a claustrophobic reaction by the user. Of course, it is highly desirable that the tendency toward such a reaction be minimized.
The magnitude of force by which conventional masks are retained upon a user's face can also influence mask tolerance because continuous application of even relatively small magnitude mechanical force on a user's face can lead to superficial trauma such as bruising and skin breakdown.